AJAX (Asynchronous JAvascript + Xml) or empovered JavaScript increases the functionality of a webpage. In a nutshell, AJAX is a mix of technologies that lets you get rid of the page reloads. AJAX is not new. The heart of AJAX is the JavaScript
XMLHttpRequest object invented by Microsoft in 1999.
Because JavaScript is used when the client talks with the server, you have to fight with browser inconsistencies. AJAX-specific pages don't work on browsers without JavaScript, they can't easily be bookmarked and search engines don't always know to parse them.
The pages are not unique, since parts of them are updated in the background. That implies obvious problems for the SE bots. Yous should be aware of this since more and more companies use AJAX technologies on their web pages. XML is an important element in the AJAX technology and there are a lot of technologies that empovers XML. Some of them are:
CSS is also an important element in the technology, even if it is not needed. A lot use PHP as server language and MySQL as database platform, but any server language and SQL database plattform may be used to create AJAX functionality.